In a modern thermal ink-jet printhead device, resistors used to propel bubbles of ink toward the paper substrate must be able to fire for millions of times without failure. In thermal printhead printing, the purity and chemical structure of the dye in the ink can radically affect the printhead operation, resulting in resistor failure or nozzle clogging.
Changing the cation of the dye molecule improves the solubility of the dye molecule in the solvent, which prevents crusting (clogging of the printhead nozzle from dye precipitation during storage). Selection of the proper cation can also significantly improve resistor life of the printhead. Substitution of FD&C Blue Dye #1 improves resistor life from about 13 million firings to about 25 million firings by changing the cation associated with the dye from sodium to triethanol amine.
In one process developed by the assignee of the present application, such cation substitution is achieved by reverse osmosis (ultrafiltration). The process is quite useful for purification of the dye. However, while producing highly acceptable dyes (in which the extend of cation substitution is controlled), reverse osmosis requires an expenditure of processing time operating at pressures of about 100 to 300 psi that may be unacceptable for some manufacturing processes.
Accordingly, a need remains for a more rapid process for improving the properties of dyes used in ink-jet printing.